Apparatus and method for finishing workpieces

ABSTRACT

A tumbling machine having an endless belt arranged so that the top run of the belt defines with a pair of side walls a V-shaped tumbling chamber in which the mixture of abrasive media and the workpieces are loaded so that at one side of the chamber the workpieces are caused to travel upwardly to a high point, then flow down towards the opposite side of the chamber where they are again conveyed by the belt around the apex of the V.

United States Patent 1191 Davidson 1 1 -3, 71,4 1 1 Feb. 13, 197

[54] APPARATUS AND METHOD FOR FINISHING WORKPIECES [75] Inventor:Richard L. Davidson, Sturgis, Mich.

[73] Assignee: The Grav-l-Flo Corporation, St.

Joseph County, Mich.

221 Filed: Dec.31,1970

21 Appl. N01: 103,266

[52] US. Cl ..5l/163, 51/313 [51] Int. Cl. ..B24b 31/10 [58] Field ofSearch ..51/163,316, 313

[56] References Cited V UNITED STATES PATENTS 1,224,191 5/1917 Medgyes..51/l63 2,538,242 1/1951 Hannon ..5l/163 2,523,304 9/1950 Johnson..5l/163 X 3,161,997 12/1964 Balz .51/3 16 FOREIGN PATENTS ORAPPLICATIONS 1,168,448 12/1958 France ..51/l63 559,869 3/1944 GreatBritain ..5 H163 Primary Examiner-Harold D. Whitehead Attorney-Barnes,Kisselle, Raisch & Choate 5 7 ABSTRACT A tumbling machine having anendless belt arranged so that the top run of the belt defines with apair of side walls a V-shaped tumbling chamber in which the mixture ofabrasive media and the workpieces are loaded so that at one side of thechamber the workpieces are caused to travel upwardly to a high point,then flow down towards the opposite side of the chamber where they areagain conveyed by the belt around the apex of the V.

17 Claims, 6 Drawing Figures PAIENTEDFEB 1 3 I975 sum 1 or 2 x i: x x xx x ATTORNEYS 3,715,840 sum 20F 2 PATENTED FEB 1 3 I973 5r F/ G. 5 wawa/ATTORNEYS APPARATUS AND METHOD FOR FINISHING WORKPIECES This inventionrelates to an apparatus and method for surface finishing of metalworkpieces.

Small workpieces are frequently deburred and/or polished on a productionbasis in tumbling barrels or vibratory finishing machines. Both of thesetypes of machines have recognized shortcomings with respect to the rateof metal removal and the quality of the finish obtainable on the surfaceof the workpiece.

The object of the present invention resides in the provision of anapparatus and method for obtaining a high quality finish on workpiecesin a minimum amount of time.

More specifically, the invention contemplates the finishing ofworkpieces by tumbling them with an abrasive or polishing media in achamber having fixed side walls and a V-shaped bottom wall formed by thetop run of an endless belt driven in one direction such that the mass ofworkpieces and finishing media are caused to travel in said chamber in amanner which promotes a high metal removal rate with a minimum ofimpingement and a maximum of rubbing or burnishing action.

The machine of the present invention is further characterized by theprovision of simple and expedient means for discharging the workpiecesand the finishing media from the machine by merely reversing thedirection of belt travel and drawing the top run of the belt taut.

Other features and advantages of the present invention will becomeapparent from the accompanying disclosure and drawings, in which:

FIG. 1 is a side elevational view of a finishing machine according tothe present invention.

FIG. 2 is a top view thereof.

FIG. 3 shows the machine as viewed from the discharge end thereof.

FIG. 4 is a fragmentary sectional view of a portion of the machine.

FIG. 5 is a diagrammatic view showing the manner in which the mass ofmedia and workpieces are caused to travel in the machine of the presentinvention.

FIG; 6 is a fragmentary perspective view within the chamber ofthemachine showing the endless belt and the mass of finishing mediaandworkpieces.

Referring to FIGS. 1 through 3, the base 10 of the machine comprises, aU-shaped stanchion having a pair of laterally spaced upright supports 12(FIG. 3) on whichthe. spaced apart side walls 14 of the machine housingare mounted. As shown in FIG. 1, each side wall 14 has a downwardlysloping upper edge 16 and two generally converging side edges 18', 20.The machine housing includes a bottom wall 22 extending between thelower portions of side walls 14 and forming a drain trough at the lowerend of the machine which slopes downwardly into a sump 24.

Two drive pulleys 26,28 are journalled between side walls 14 at oppositeends of themachine and adjacent the upper edges of the side walls. Anendless belt 30 is trained around pulleys 26,28 and around a pair ofidler pulleys 32. A belt tightener in the form of pivotally supportedarm 34 carrying a roller 36 at its free end is also provided. The belttightener is adapted to'be actuated by a hydraulic cylinder 38 betweenthe two positions shown in FIG. 1.

On the inner surface of one side wall 14 there is fixedly secured a wearplate 42. A second wear plate 44 is mounted on the other side wall 14for adjustment toward and away from wear plate 42 so that the two wearplates are engaged by the opposite side edges of endless belt 30 andwear plate 44 can be adjusted laterally to compensate for wear in thewidth dimension of belt 30. A generally V-shaped belt guide 46 which isnarrower than belt 30 is secured to the two side walls 14 and extendsbetween the two wear plates 42,44. In FIG. 4 the two legs of theV-shap'ed belt guide are designated 48, 50 and the rounded apex of the Vis designated 52. In FIG. 1 the upper edges of the wear plates 42,44 aredesigned 51 and in FIG. 4 the opposite side edges of the wear plates aredesignated 53,55. At the rounded apex 52 the guide plate is providedwith a plurality of drain openings 54. It will be observed that leg 48of guide plate 46 extends along a line generally tangent to pulley 26and leg 50 extends along a line generally tangent to pulley 28. Leg 48is more steeply inclined than leg 50. In the embodiment illustrated leg48 is inclined to the vertical at an angle of about 22 nd leg 50 isinclined to the vertical at an angle of about 4. As will be explainedhereinafter, these angles can b varied within a limited range dependingupon the speed at which the belt is driven.

Pulleys 26,28 are keyed to shafts each having a s rocket 56 on one endthereof. The output shaft of a s eed reducer unit 58 has a pair ofsprockets 60 keyed t ereto. A pair of chains 62 are trained around bothp ir of sprockets 60 and 56 so as to rotate the two pulle s 26,28 at thesame speed and in the same direction. B It 30 is driven by thefrictional engagement of pulleys 26,28 with the belt. Speed reducer unit58 is preferably ad ustable so as to vary the speed of the belt asdesired.

\ he diagrammatic showing in FIG. 5 illustrates the copfiguration of thetop run 300 of belt 30 and the botto l run30b of the belt while themachine is in operation The locations of drive pulleys 26,28 and idlerpulley'sL32 are determined in relation to the length of belt 30 and thesize of the load which the machine is designed to handle such that theupper run 30a of the belt assumes a configuration which generallyparallels the shape of guide plate 46 and such that the upper run of thebelt will be spaced slightly from guide plate 46 as indicated by theclearance space 64in FIG. 4. Thus, with'the machine operating in themanner, illustrated in FIG. 5 the upwardly travelling portion of'the toprun 30a of the belt is inclined to the vertical at an angle of about 22and the downwardly travelling portion of the top run 30a of the belt isinclined to the vertical at an angle of about 44. It will be appreciatedhowever that FIG. 5 actually illustrates the dynamic, not the static,condition of the belt. Furthermore, it will be appreciated that thefunction of guide plate 46' is merely to prevent the top run 30a of thebelt from swaying. Under ideal operating conditions guide plate 46 willbe spaced throughout its extent from the underside of the top run 30a ofthe belt.

In FIG. 6 the workpieces being processed are illustrated asdished-shaped discs 66 and the polishing media or chips are in the formof cones 68 molded from a mixture of a binder, such as a synthetic resinor a ceramic, and abrasive. The use of such preformed synthetic chips,as distinguished from natural stone chips, is very desirable becausenatural stone chips tend to splinter whereas the synthetic chips merelywear down in size and are therefore not apt to become wedged between theedges of belt 30 and wear plates 42,44. For some types of finishingoperations (polishing, for example, where chips are slippery) it isdesirable to have angled cleats 70 on the belt to assist in elevatingthe mass by means of the upwardly travelling portion of the top run ofthe belt.

Nozzle 72 is illustrated in FIG. 1 and is located above and slightlyinwardly of the upper end of the portion of the belt run travellingupwardly. The nozzle is utilized for.directing a spray of water or watercontaining a nonabrasive detergent over the mass of workpieces andabrasive media as it reaches the upper end of the upward travel. Asindicated in FIG. 5 nozzle 72 is connected by a conduit 74 with theoutlet of a pump 76 having its inlet connected to sump 24 above thebottom thereof. Thus, with this arrangement the water spray issuing fromnozzle 72 cleans the parts and media and then drains into the sumpthrough the drain holes 54 at the lower end of belt guide 50. The finegrindings off f the metal workpieces and the media preforms settles nsump 24 and the substantially uncontaminated water is recirculated backto nozzle 72. Flushing of the W kpieces and media is important in orderto maintai a clean mass within the chamber of the machine. It ser es toaccelerate the cutting action of the abrasive me la on the workpieces.

The spray nozzle 72 also clears the belt of abrasive chips andworkpieces that might otherwise adhere to the belt and become dischargedover pulley 26. i

In operation the machine is charged with a loa I of workpieces to befinished and an abrasive media, S i-ICII as the preformed chips 68. Whenpulleys 26,28 are driven in a counterclockwise direction as viewed inFIG. the mass assumes the configuration show in FIG. 5. Generallyspeaking, the moving mass be considered as divided into several areas orzones lhe most active zone, designated A, may be referred tip as theslide zone wherein the parts and media gra i ate from the vicinity ofhigh point 78 to the vicinity of low point 80 adjacent the downwardlytravelling portion of the belt. The downward slope of the slide area 80depends upon the shape and surface characteristics of the media andparts. Generally speaking, the slide area inclines downwardly at a fixedangle of between 25 to 35. The second most active zone in the mass isdesignated B in FIG. 5 and comprises a layer of the mass adjacent theupper run of the belt. This portion of the mass is active not onlybecause it is being positively driven by the belt, but also because theside walls of the chamber in which the mass is located, namely, wearplates 42,44, remain stationary while the belt is carrying the mass,thus causing additional friction between the layer of the material ateach of the sides of the chamber and the material in the center of themass. The next most active zone is designated C in FIG. 5 and comprisesthe annular teardrop shape portion surrounding zones A and B. Thisactivity, that is, the relative movement between the parts and themedia, in this area is less than in areas A and B. The center area D maybe referred to as the dead cone since there is considerably lessactivity in this zone than in the other zones. However, the parts do notremain stagnant in area D. workpieces and media continually work intoand out of this area from and into the other areas represented in FIG.5.

One of the features of the present invention resides in the fact thatarea D is relatively small in comparison to the size of the mass. Thismay be explained by the fact that substantial activity occurs in areas Band C as a result of the drag effect on the parts and media by thestationary wear plates while the mass is being positively driven by thebelt.

The slope of the upwardly travelling portion of the belt and the speedof the belt are controlled so that as the parts approach the high end ofthe slide zone A they gently flow around the high point A and gravitatesmoothly down toward the low point 80. If the slope of the upwardlytravelling portion of the belt is too steep the workpieces roll out ofthe mass media too freely in the vicinity of high point 78 and simplyroll down the slide area A over the mass of abrasive media. Thisproduces relatively little work on the workpieces and prolongs theduration of the finishing cycle. On the other hand, if the slope of theupward travelling portion of the belt is not great enough, the partstend to churn and remain too long in the high point area 78 where thework being performed on the parts is substantially less than in theslide area A. An inclination of about 22 for this portion of the belt ispreferred but inclinations between 17 to 27 are possible.

The slope of the downwardly travelling portion of the top run of thebelt is determined such that the slope of the slide zone intersects theplane of the belt at an included angle of less than 90. This has beenfound to be desirable to avoid impingement and build-up of the parts andmedia around the low point of the slide zone A. lmpingement should beavoided as much as possible in order to obtain the best quality finish.In the machine of this invention impingement is also avoided by reasonof the fact that the downwardly travelling portion of the belt is at afixed angle (as distinguished from a changing angle as in the case of astraight sided tumbling barrel) and the belt speed can be controlled sothat the workpieces flow or fold smoothly into the portion of the massbeing driven downwardly by the belt. While an inclination of about 44 tothe vertical is preferred, inclinations of between about 40 to 50 arepossible.

An extremely important feature of the present invention has to do withthe length of a slide zone A in relation to the size of the mass and thesize of the least active area D. Slide zone A in a machine of thepresent invention is substantially greater than the slide area of atumbling barrel designed to accommodate the same size load and at thesame time the size of the inactive area D in the machine of the presentinvention is substantially smaller than the size of the tumbling barreldesigned to accommodate the same load. It follows, of course, that theslide area of a given tumbling barrel can be increased by increasing thediameter of the barrel but it must be remembered that as the diameter ofthe barrel increases the size of the inactive areain the barrel alsoincreases.

In order to obtain values showing the relative rates of cut and thequality of finish obtainable with a machine of the present invention ascompared with a vibratory finishing machine and a tumbling barrel, threeidentical loads of small door handles and preformed abrasive chips wererun for a period of 4 hours in each of the three machines. The loadconsisted of I70 lbs. of 9/16 inch X 9/16 inch cone-shaped chips madeofpolyesther resin and silica abrasive along with 45 lbs. of zinchandles. A nonabrasive detergent compound was used at the rate of 1ounce per gallon ofwater.

The tumbling machine had an actagon shaped cylinder I6 inches long and30 inches across the flats, and, thus, had an optimum capacity of about3.l cubic feet. The vibratory finishing machine also had a 3.1 cubicfoot capacity. The tumbling barrel was rotated at 20 r.p.m. and thefrequency of the vibratory finishing machine was 2,100 r.p.m. with anamplitude of oneeighth inch. The machine according to the presentinvention had a width of 8 inches and a radius of inches at the lowerrounded end of the V-shaped belt. The two drive pulleys 26,28 had adiameter of 10 inches and were driven at 58 r.p.m. producing a linealspeed of the belt of about l,800 feet per minute. When the machine wasoperated with a load of 3.1 cubic feet of chips and handles, the massassumed the configuration and relative proportions shown in FIG. 5. The

results of these tests are shown in Table I.

TABLE 1 Media Part Media loss loss loss per oz. of metal loss TumblingBarrel 2 lbs. I A 02. 2L3 oz. Vibratory 6 lbs. Machine I0 02. 4 oz. 26.5oz. Endless Belt 6 lbs. Machine 9 oz. l6.l oz.

. operating the machine with a mixture of workpieces and abrasive media.After the desired initial finish is obtained, a polishing compound canbe added to the mass in order to obtain a smooth, high luster finish onthe workpieces. The successive operations can be performed withoutremoving the mass from the machine or without even stopping theoperation of the machine. This feature of the present inventionsubstantially reduces labor costs in comparison with the time and workrequired for obtaining a high luster, smooth finish on workpieces in atumbling barrel.

Referring to FIG. I, it will be noted that when cylinder 38 is actuated,arm 34 is pivoted from its raised to the lowered position. Since roller36 engages the inside face of the lower run of belt 30, the top run 300of the belt la caused to gradually shorten in length to it finally tautcondition shown at 02 In FIG. I. Thus, if the direction of rotation ofthe belt is reversed, that is, pulleys 26,28 rotated clockwise insteadof counterclockwise, as the top run of the belt approaches its tautposition the mass of workpieces and media is automatically dischargeddownwardly over pulley 28 onto a receiving conveyor or other collectorand separating means guiding the belt around said rollers such that the7 top run of the belt is slack and assumes a generally V- shapedconfiguration between the rollers which is nonsymmetrical about avertical axis through the apex of the V, the side of the V adjacent thehigher roller being moresteeply inclined than the other side of the V, apair of fixed side plates disposed one adjacent each edge of the beltand cooperating with the top run of the belt to define a generallyV-shaped chamber for containing a mass of workpieces and finishing mediaand means for driving the belt in one direction such that the mass ofmedia and workpieces is caused to flow in said chamber in a pathupwardly along said moresteeply inclined side of the V-shaped chamber inthe direction of the upwardly travelling portion of the top run of thebelt, then downwardly across the chamber in the direction toward thedownwardly travelling portion of the upper run of the belt at the lesssteeply inclined side of the V and then downwardly along saidlast-mentioned side ofthe V and around the apex of the V to the upwardlytravelling portion of the belt, the apex of said V being curved in anupwardly concave direction and the sides of said V being generally flat,the linear extent of said curved apex being small relative to the linearextent of the sides of said V.

2. A machine as called for in claim I wherein said belt driving meanscomprises both of said rollers.

3. A machine as called for in claim I wherein said belt driving meanshave a driving connection with said belt adjacent each of said rollers.

4. A machine as called for in claim I wherein said guide means includesmeans on the underside of the top run of the belt for maintaining theapex of the V- shaped top run of the belt in a generally fixed positionbetween said rollers.

5. A machine as called for in claim 1 wherein said guide means aredisposed on the underside of the top run of the belt and are arranged ingenerally V-shaped fashion with one of the legs of the V adjacent theupwardly travelling portion of the top run of the belt and and otheradjacent the downwardly travelling portion ofthe top run of the belt.

6. A machine as called for in claim I wherein the upwardly travellingportion of the top run of the belt is inclined to the vertical at anangle of between about 17 and 27.

7. A machine as called for in claim 6 wherein the downwardly travellingportlon of the top run of the belt is inclined to the vertical at anangle of between about 40 to 50.

8; A machine as called for in claim 1 including belt tightening meansfor optionally removing said slack from the top run of the belt to causesaid top run of the belt to extent substantially straight in adownwardly inclined angle between said upper and lower rollers.

9. A machine as called for in claim 8 including means for driving thebelt such that said straight top run is travelling downwardly in thedirection from said upper to said lower roller to discharge the contentsof said chamber.

10. A method of finishing workpieces which comprises, charging a mixtureof abrasive media and workpieces into a chamber having fixed side wallsand a generally V-shaped bottom wall defined by the upper run of anendless belt causing the major portion of said upper run of the belt toassume an angle substantially more steeply inclined to the vertical atone side of the V than at the other side ofthe V and driving said beltin a direction such that the upper run thereof is travelling upwardly atthe more steeply inclined side thereof and downwardly at the lesssteeply inclined side thereof thereby causing said mass to flow in saidchamber in a path extending upwardly in a direction generally parallelto the more steeply inclined, upwardly travelling portion of said bottomwall, then downwardly across said chamber toward the less steeplyinclined, downwardly travelling portion of the bottom wall, thendownwardly in the direction of travel of the less steeply inclined,downwardly moving portion of the bottom wall and around the apex of theV to the upwardly travelling portion ofthe bottom wall.

11. The method called for in claim 10 wherein said mass is caused totravel in said upward and downward directions at generally fixed anglesinclined relative to the vertical.

1 2. The method called for in claim 10 wherein at least the majorportion of said mass is caused to travel in said upward direction at agenerally fixed angle of between 17 and 27 to the vertical.

13. The method called for in claim 12 wherein at least the major portionof said mass is caused to travel in said downward direction toward thedownwardly travelling portion of the bottom wall at a generally fixedangle to the horizontal of about 25 to 35.

14. The method called for in claim 13 wherein at least the major portionof said mass is caused to travel in said direction of said downwardlymoving portion of the bottom wall at a generally fixed angle of about 40to 50 to the vertical.

15. The method called for in claim 12 wherein the direction of travel ofthe mass in said downwardly direction toward the downwardly movingportion of the bottom wall and the direction of travel of the mass inthe direction of the downwardly moving portion of the bottom wallintersect with an included angle of less than 16. A machine as calledfor in claim 1 including means disposed adjacent the upper roller andthe upper run of the belt an operable to prevent the workpieces andmedia in the chamber from being carried upwardly over the top roller asthe belt travels thereover and for assisting the workpieces and media toflow in said path downwardly across said chamber.

17. A machine as called for in claim 16 wherein said last-mentionedmeans comprises nozzle means for directing pressurized liquid streamsagainst the top run of the belt in said chamber and adjacent the upperroller.

i i i i i

1. In a machine for finishing workpieces the combination comprising, apair of rollers spaced apart on parallel axes, one of said rollers beinglocated in a plane above the other roller, an endless belt trainedaround said rollers, said belt having a length substantially greaterthan twice the distance between the roller axes, means guiding the beltaround said rollers such that the top run of the belt is slack andassumes a generally V-shaped configuration between the rollers which isnonsymmetrical about a vertical axis through the apex of the V, the sideof the V adjacent the higher roller being more steeply inclined than theother side of the V, a pair of fixed side plates disposed one adjacenteach edge of the belt and cooperating with the top run of the belt todefine a generally V-shaped chamber for containing a mass of workpiecesand finishing media and means for driving the belt in one direction suchthat the mass of media and workpieces is caused to flow in said chamberin a path upwardly along said more steeply inclined side of the V-shapedchamber in the direction of the upwardly travelling portion of the toprun of the belt, then downwardly across the chamber in the directiontoward the downwardly travelling portion of the upper run of the belt atthe less steeply inclined side of the V and then downwardly along saidlast-mentioned side of the V and around the apex of the V to theupwardly travelling portion of the belt, the apex of said V being curvedin an upwardly concave direction and the sides of said V being generAllyflat, the linear extent of said curved apex being small relative to thelinear extent of the sides of said V.
 1. In a machine for finishingworkpieces the combination comprising, a pair of rollers spaced apart onparallel axes, one of said rollers being located in a plane above theother roller, an endless belt trained around said rollers, said belthaving a length substantially greater than twice the distance betweenthe roller axes, means guiding the belt around said rollers such thatthe top run of the belt is slack and assumes a generally V-shapedconfiguration between the rollers which is nonsymmetrical about avertical axis through the apex of the V, the side of the V adjacent thehigher roller being more steeply inclined than the other side of the V,a pair of fixed side plates disposed one adjacent each edge of the beltand cooperating with the top run of the belt to define a generallyV-shaped chamber for containing a mass of workpieces and finishing mediaand means for driving the belt in one direction such that the mass ofmedia and workpieces is caused to flow in said chamber in a pathupwardly along said more steeply inclined side of the V-shaped chamberin the direction of the upwardly travelling portion of the top run ofthe belt, then downwardly across the chamber in the direction toward thedownwardly travelling portion of the upper run of the belt at the lesssteeply inclined side of the V and then downwardly along saidlast-mentioned side of the V and around the apex of the V to theupwardly travelling portion of the belt, the apex of said V being curvedin an upwardly concave direction and the sides of said V being generAllyflat, the linear extent of said curved apex being small relative to thelinear extent of the sides of said V.
 2. A machine as called for inclaim 1 wherein said belt driving means comprises both of said rollers.3. A machine as called for in claim 1 wherein said belt driving meanshave a driving connection with said belt adjacent each of said rollers.4. A machine as called for in claim 1 wherein said guide means includesmeans on the underside of the top run of the belt for maintaining theapex of the V-shaped top run of the belt in a generally fixed positionbetween said rollers.
 5. A machine as called for in claim 1 wherein saidguide means are disposed on the underside of the top run of the belt andare arranged in generally V-shaped fashion with one of the legs of the Vadjacent the upwardly travelling portion of the top run of the belt andand other adjacent the downwardly travelling portion of the top run ofthe belt.
 6. A machine as called for in claim 1 wherein the upwardlytravelling portion of the top run of the belt is inclined to thevertical at an angle of between about 17* and 27* .
 7. A machine ascalled for in claim 6 wherein the downwardly travelling portion of thetop run of the belt is inclined to the vertical at an angle of betweenabout 40* to 50* .
 8. A machine as called for in claim 1 including belttightening means for optionally removing said slack from the top run ofthe belt to cause said top run of the belt to extent substantiallystraight in a downwardly inclined angle between said upper and lowerrollers.
 9. A machine as called for in claim 8 including means fordriving the belt such that said straight top run is travellingdownwardly in the direction from said upper to said lower roller todischarge the contents of said chamber.
 10. A method of finishingworkpieces which comprises, charging a mixture of abrasive media andworkpieces into a chamber having fixed side walls and a generallyV-shaped bottom wall defined by the upper run of an endless belt causingthe major portion of said upper run of the belt to assume an anglesubstantially more steeply inclined to the vertical at one side of the Vthan at the other side of the V and driving said belt in a directionsuch that the upper run thereof is travelling upwardly at the moresteeply inclined side thereof and downwardly at the less steeplyinclined side thereof thereby causing said mass to flow in said chamberin a path extending upwardly in a direction generally parallel to themore steeply inclined, upwardly travelling portion of said bottom wall,then downwardly across said chamber toward the less steeply inclined,downwardly travelling portion of the bottom wall, then downwardly in thedirection of travel of the less steeply inclined, downwardly movingportion of the bottom wall and around the apex of the V to the upwardlytravelling portion of the bottom wall.
 11. The method called for inclaim 10 wherein said mass is caused to travel in said upward anddownward directions at generally fixed angles inclined relative to thevertical.
 12. The method called for in claim 10 wherein at least themajor portion of said mass is caused to travel in said upward directionat a generally fixed angle of between 17* and 27* to the vertical. 13.The method called for in claim 12 wherein at least the major portion ofsaid mass is caused to travel in said downward direction toward thedownwardly travelling portion of the bottom wall at a generally fixedangle to the horizontal of about 25* to 35*.
 14. The method called forin claim 13 wherein at least the major portion of said mass is caused totravel in said direction of said downwardly moving portion of the bottomwall at a generally fixed angle of about 40* to 50* to the vertical. 15.The method called for in claim 12 wherein the direction of travel of themass in said downwardly diRection toward the downwardly moving portionof the bottom wall and the direction of travel of the mass in thedirection of the downwardly moving portion of the bottom wall intersectwith an included angle of less than 90*.
 16. A machine as called for inclaim 1 including means disposed adjacent the upper roller and the upperrun of the belt an operable to prevent the workpieces and media in thechamber from being carried upwardly over the top roller as the belttravels thereover and for assisting the workpieces and media to flow insaid path downwardly across said chamber.